With rotary carousels on labeling and capping machines, it is usually the carousel rotation that imparts, through a mechanical cam, the motion to the bottle holder platter or capping chuck that
regulates the tightening torque applied with a magnetic clutch. Often times, however, these mechanical cam systems have a number of shortcomings.
Efficiency can be difficult to achieve because the mechanical couplings can require complex and costly installation procedures as well as constant maintenance. They can also be noisy. Another concern can be the limited flexibility and scalability of these systems, both during the design stage and for machines already in service.
Recent technological advances let mechanical cams be replaced with electronic cams. In one capping application, each platter or chuck is driven by an on-board electric motor, the 57 Harmonicas, from Elmo Motion Control, Ltd. The motor is coupled to the relative utility through belts, pulleys or gear trains to achieve the required reduction ratio, and it communicates with a
separate machine control system that manages operation of all the axes.
An encoder sits in the static part of the machine and sends the location information of the carousel’s central axis using the CANopen protocol. Thus, the axes know the location of the carousel without additional wiring.
In this labeling application, an electronic cam replaces a mechanical cam, enhancing the machine’s flexibility.
CANopen was selected because this protocol can handle the volume of data traffic. Through the electronic CAM programs on the drives, the update rate of location data increased from 4 ms/point to 2 ms/point while reducing the network baud-rate from 15 MHz to 500 KHz.
Instead of an encoder, this system could be outfitted with a resolver in a compact drive. This arrangement would enable the engine to be placed in the bottle axis without a strap. At this stage the engine would receive a shock when the bottle is pressed, which would eliminate other drives that are unable to withstand these compact and resolver conditions.
The Harmonica is an intelligent compact digital servo drive for dc brush, brushless, and linear motors. It can deliver a peak of 2200 W of power and 1100 W of continuous power. It can operate in position, velocity, and current modes with a range of feedback and I/O options.
The ECAM programming mode of the Harmonica drives increases an existing machine’s flexibility. For example, it allows the bottle’s movement profile to be changed by altering parameters without making a mechanical change, such as changing the bottle turning speed based on the bottle’s radius.
The use of an electronic cam offers other advantages. One is format flexibility because the format is managed electronically, which allows modifications to the machine operating cycle both during the design stage and for machines already in service. Other advantages include a reduction in system complexity and the ability to work in extreme environments.
Elmo Motion Control, Ltd.
:: Design World ::
Filed Under: Drives (servo) + amplifiers, Motion control • motor controls
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